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- Unmanned aerial vehicle safety assessment modelling through petri NetsPublication . Gonçalves, P.; Sobral, José; Ferreira, L. A.Currently we are facing an increasing trend of use of Unmanned Aerial Vehicles (UAV) in various activities both civilian and military. Although there is no legal framework for the operation of these systems, regulatory authorities require the demonstration of a safety level equivalent to manned aircraft. It is known the high vulnerability of the UAV not only to unexpected failures of their systems but also to the environment. The purpose of this paper is to present a safety assessment process modelling of a UAV by Petri Nets, that can be accepted by certifying bodies, considering the recommendations of STANAG 4671 UAV Airworthiness Requirements Specification (USAR) for analysis of fault conditions that lead to the most feared events. It is intended to show through the use of Petri Nets the frequency that the UAV enters the identified states described as most feared events; the ability of the UAV to react after being in a fault situation to the inputs of the operating crew in order to enhance trust and to facilitate the operation authorization process in UAV operations. The results obtained allowed to identify and to define critical areas and corrective actions that will lead to an acceptable level of risk for the regulatory authority.
- Establishment of an initial maintenance program for UAVs based on reliability principlesPublication . Gonçalves, Paula; Sobral, José; Ferreira, LuísPurpose - The purpose of this paper is to illustrate how to develop a methodology to set up an initial maintenance program for unmanned aerial vehicles (UAVs) following the well-known Steering Maintenance Group logic method (MSG-3) and taking into account safety concerns based on items probabilities of failure. That is why it is stated that maintenance program is based on reliability principles. Design/methodology/approach - The proposed methodology follows the MSG-3 framework applied to civil aircraft but where the determination of each probability of failure is achieved applying a morphological analysis. These probabilities are then affected by some factors to calculate the adjusted values to the specific conditions (design, operation and environment) under which the system is expected to operate. Findings - Main findings are related to the applicability of the morphological analysis on the developing of an initial maintenance program when there is a lack of data that disable the establishment of a coherent maintenance program. Research limitations/implications - Limitations are related to the absence of a legislative framework consensual in Europe for certification of UAVs and the lack of data concerning UAVs failure modes, causes and their probability of failure. Practical implications - The developed work and the methodology proposed may be useful for UAVs maintenance program engineers and technicians when developing new systems. Originality/value - The originality is based on the use of morphological analysis for UAVs to determine the items probabilities of failure when there is a no-data problem. Based on the referred analysis, it is possible to create an initial maintenance program for UAVs.